1. Field of the Invention
This invention generally relates to heating appliances and, more particularly, relates to gas-fueled heating appliances, both ventless, which vent combustion gases directly into the room in which the appliance is installed and vented, which vent combustion gases to atmosphere.
2. Description of the Related Art
Gas-fueled heating appliances, such as fireplaces, stoves, and fireplace inserts, have the cleanest exhaust of any combustion process and typically include a combustion chamber, or firebox, which is provided with a source of flammable gas. The flammable gas is then combusted to provide heat and aesthetic value to the room in which the appliance is installed. The combustion typically produces carbon monoxide, carbon dioxide, water, oxygen, nitrogen, nitrogen oxide, and carbon soot, which are vented away from the fireplace and to the outside environment through a flue network or chimney. The major constituents are oxygen, nitrogen, carbon dioxide, and water with significantly lower levels of carbon monoxide, nitrogen oxides, and carbon soot. The mercaptan odorant found in gas fuel oxidizes and forms sulfuric oxides. Although such gases are vented to atmosphere, causing no serious problems in the space adjoining the appliance, increasing concerns about the environment may bring this process under heavy scrutiny and eventual regulation.
In certain locations, it is desirable to have an appliance capable of operating without venting to the outside environment. Therefore, gas appliances have been designed which are clean burning but "unvented" in that the gas combusts and the products of the combustion are allowed to enter the room in which the appliance is installed. With such designs, a chimney or flue network is not necessary and consequently such designs can be placed in many locations which would otherwise not be able to accommodate a vented appliance.
Because such designs allow combustion gases to enter the room in which the fireplace is installed, any combustion products, such as carbon monoxide, and airborne particulates, are also exhausted from the appliance directly into the room in which the appliance is located.
In addition, with conventional unvented appliances, the combustion gases rise within the firebox and heat the top wall of the firebox before exiting into the room in which the fireplace is installed. If the heat is not controlled, this can potentially damage the top wall of the firebox or a mantle associated therewith.
U.S. Pat. No. 5,054,468, issued to Moon, discloses an unvented gas-fueled fireplace heater which vents all combustion gases and airborne particulates directly into the room in which the heater is installed, but does not include any means for reducing undesirable emissions.
U.S. Pat. No. 5,139,011, also issued to Moon, discloses an unvented gas-fueled fireplace heater which vents combustion gases and particulates directly to the ambient room air, and further includes a sensor which detects a low oxygen level and a gas supply switch which is activated by the oxygen sensor.
Early attempts at ventless appliances suffer from drawbacks such as: 1) water build-up in the space, 2) acid gases, such as nitrogen oxide and sulfuric oxide, are discharged into the space potentially causing respiratory distress and corrosion in the home, 3) excessive oxygen consumption, and 4) excessive build-up of carbon monoxide levels in the space.